Figure 1. Anatomy of graft rejection and tolerance.

(A) Vicious cycle of graft rejection. Graft-specific Tconvs enter the graft, leading to inflammation and tissue damage. Inflammatory antigen-presenting cells (APCs) enter the draining lymph node to activate more graft-specific cells. Graft-specific Tregs are too few to effectively control this process. (B) Increasing Tregs combined with reduction of graft-specific T cells allow Tregs to dominate in the graft and prevent recruitment and activation of effector T cells. Tolerogenic APCs enter the draining lymph node to expand graft-specific Tregs and prevent expansion of graft-specific T cells to maintain tolerance.